The training program, consisting of walking on a treadmill according to an interval-training pattern, is carried out 3 times weekly for 12 weeks. If patients miss a training session, the program is prolonged until 36 workouts are carried out. The initial duration of training sessions is 30 minutes. During the first week, training consists of 5 workloads of 3 min; between workloads patients walk with half-speed for 3 min. Exercise duration is gradually increased to 4 x 5 min a day in the second week, 3 x 8 min in the third, 3 x 10 min in the fourth and 2 x 15 min in the fifth week. In the sixth and further weeks, exercise is progressively increased to 30, 32 and 36 min and is carried out without interruption. Training intensity corresponds to the speed necessary to reach a lactate concentration of 2.5 ± 0.5 mmol/l in capillary blood slightly above the aerobic threshold. Heart rate during training is controlled by a heart-rate monitor. As lactate concentration sinks below 2.0 mmol/l or exercise heart rate decreases by more than 5/min as a result of training adaptation, treadmill speed is increased by 0.5 km/h or elevation is increased by 3% to maintain training intensity. We have previously shown that this training protocol leads to a substantial increase of physical performance in short time. During training patients are continuously supervised by a physician.